It is proposed to study racial and ethnic differentiation in U.S. cities in 1880, with a particular emphasis on the relationships between people and places. The project will use full-count census data from the U.S. Census of Population in 1880 to create a wide range of summary files, aggregating information at levels of geography including the enumeration district, city or town, county, metropolitan region, and state. For all 98 separately identified cities in 1880, analyses will investigate the effects of city and group characteristics on aggregate patterns of separation or assimilation. For the largest 25 cities, Geographic Information System (CIS) maps will be developed for all variables in 1880 at the level of enumeration districts. In these cities, measures of spatial clustering will be used to identify ethnic neighborhoods. Models will be estimated analyzing what personal and household characteristics of individuals are associated with living within (or outside) ethnic neighborhoods and working within (or outside) ethnic employment niches. A separate sample of 37,000 men with records matched between 1870 and 1880 will be the basis for models in which key characteristics in 1870 will be introduced. An important component of the project will be the creation and dissemination of public-use data files. These will include pretabulated summary files based on individual data, CIS boundary files for enumeration districts in major cities, and a multilevel dataset that combines individual and household data for a 1 percent sample of the population with information about the places where they live. This new data infrastructure will expand opportunities for social scientists of all disciplines on a key period in American history: a time when the Western frontier was still being settled, when the transformation of the country from an agricultural to an industrial economy was only beginning, when African Americans had only recently been released from slavery, when cities like Chicago were in their infancy and older cities like New York were still receiving their first waves of German and Irish immigrants, and the nation was on the verge of the next great wave of population movements - of blacks from South to North, of immigrants from Southern and Eastern Europe, and Chinese and other groups from East Asia.